Various kinds of functional foods containing mainly calcium, which may be used as supplemental foods for osteoporosis or other bone-related diseases, are on the market. Currently, these calcium containing foods are mainly made from calcium carbonate, calcium lactate, calcium phosphate, or cattle bone powder, egg shells or fish bone powder (natural bone-derived calcium).
Although the relationship between the characteristics of calcium components ingested to the body and its degradation and intake inside the body is not completely solved, it is considered in general that intake of natural bone-derived calcium is distinctly superior to simple intake of calcium salts in terms of quick recovery from bone diseases. However, there is a disadvantage in the commercially available natural calcium based foods such as cattle bone powder or fish bone powder in their problematic ingestibility. That is, they are not fully degraded by gastric acid due to their coarse particles since they are made into powder by grinding.
A method was proposed in which mammal bones are decalcified using acidic solution in order to achieve efficient intake of calcium components (Japanese Laid-Open Patent Application No. 4-16165). This method basically provides calcium intake supplements or calcium replenishments in which soluble calcium is added to an acid soluble fraction obtained by decalcifying ground bone powder using an aqueous solution of inorganic acid such as hydrochloric acid, sulfuric acid and nitric acid or that of organic acid such as formic acid and acetic acid, or to a water soluble fraction obtained by adding an enzyme to the above fraction and hydrolyzing it, or to a fraction obtained by dialyzing the above fractions to remove bone-derived calcium salts.
More specifically, ground bone is suspended in an aqueous solution of pH 2-3 containing the above-mentioned inorganic acid or organic acid and the bone is decalcified by stirring for 30 min. to a few hours. Then protease (e.g. pepsin) is added to carry out enzymatic degradation and a resulting acid soluble fraction or water soluble fraction of molecular weight 3000 to 60000 Da is used as the calcium intake supplements, or the above fractions are further desalinized to produce fractions comprising a mixture of peptides and proteins and soluble calcium lactate or calcium carbonate is added thereto to produce the calcium replenishments.
On the other hand, mammal bones contain not only calcium but also physiologically active substances such as collagen proteins including peptides or polypeptides, amino acids, proteoglycan and trace amounts of bioactive elements. It is known that these substances other than calcium are also desirable supplements for bone related diseases from the point of view of enhancing physiological activity (hormone balance or activity of enterobacteria) which is very important in biological systems. Especially, it has been found that proteins such as BMP or BSP-II discovered recently are deeply involved with the formation of bone. Their use as pharmaceuticals has been studied.
In the meantime, since the above mentioned conventional method used strong acids to decalcify bone components, the physiological activity of components contained in products are lowered. Also, since physiologically active substances such as proteins and proteoglycan are denatured by heat generated during a grinding process of mammal bones, which is carried out before the decalcification process, the products do not contain natural components of the bone.